a) Field of the invention
The present invention relates to a double-walled container for transporting and storing a liquified gas or cryogenic liquid such as hydrogen, at low temperature.
More particularly, the invention relates to a double-walled container of the above mentioned type, which is light weight and of a very great size and which can be used for the international transportation of liquid hydrogen by air, sea, rail or road.
b) Brief description of the prior art
Double-walled containers comprising an inner vessel mounted within an outer insulation shell are well known and widely used for transporting and storing liquified gases. To be efficient and safe in use, such containers must comply with several structural requirements related to their conditions of use. They must also comply with national and/or international regulations on dangerous products transportation.
One of these requirements is that the thermal conduction between the outer surface of the inner vessel which is cold, and the inner surface of the outer shell, must be as low as possible. In practice, a very good insulation is difficult to achieve.
Another requirement intimately related to the previous one is the time of storing and transportation of the liquified gases within the container, when the same is handled by air, rail, road or sea. The transportation time can sometimes be very long and an autonomy at least 30 days is often required. When heat conductive materials like stainless steel are used for manufacturing the container and no insulation is provided, an autonomy of a few days only can be achieved.
A further requirement is the weight of the container that must be low. If the container is exclusively made of a heavy material like stainless steel, its size will necessarily have to be reduced, thereby reducing the amount of liquified gases to be stored and transported. This, in turn, will limit the amount of liquified gases per container and increase the transportation price. In this connection, it is worth mentioning that the standard, all steel construction double-walled containers presently in use, are usually of a small or medium size only, and have a deadweight to pay load ratio ranging between 6:1 and 8:1.
To solve this problem, it has already been suggested to manufacture double wall containers from lightweight, gastight polymeric materials. This, however, has only been made with very small containers, like those sold under the trademark THERMOS (see also U.S. Pat. No. 5,150,812).
Still another requirement is the necessity of having reliable and efficient means for mounting and supporting the inner vessel within the outer shell. Indeed, the supporting means must be devised to safely absorb all kinds of force such as acceleration, deceleration or expansion forces during transportation, due to rail or road conveyor movements, ocean disturbances and airplane take-off or landing. To position and stabilize the inner vessel within the outer shell in such a manner as to leave an insulation gap in between, it has already been suggested to use ropes, tie rods, articulated bars or slide rails. It is obvious that these constructions are not only expensive but also very complicated and heavy (see, for example, EP-A-063,714 and GB-A-1,220,251, both to MESSER GRIESHEIM G.m.b.H).